Process of electrodepositing an adherent layer of copper from copper refinery electrolyte on alloys of iron and/or nickel containing chromium



Patented June PROCESS OF ELECTRODEPOSITING AN AD- HEBENT LAYER OF COPPERFROM COP- PER REFINEBY ELECTBOLYTE ON ALLOYS OF IRON AND/OR NICKELCONTAINING GHBOMIUM Andrew Wesley, Plainfield, and Harry R. Copson,Westfield, N. 1., assignors to The International Nickel Company, Inc.,New York, N. Y., a corporation of Delaware No Drawing. Application April26, 1938,

Serial No. 204,304

6 Claims.

The present invention relates to a process of electrodepositing an'adherent coating of copper from copper refinery electrolyte on an alloyof iron and/or nickel which contains chromium, and, more particularly,to a process of coating alloys of the 80% nickel-14% chromium andstainless steel types, with an adherent layer of copper electrodepositedfrom a bath of copper refinery electrolyte.

For certain purposes, it is desirable to have a composite metal, onelayer of which is copper and another layer of which contains chromium oris constituted of a nickel-chromium-iron alloy. Considerable difficultyhas heretofore been experienced in securing good adherence between thesurface of a chromium-containing article, especially an article made ofa chromium-containing alloy of nickel and/or iron of the stainless type,and the surface of a copper layer when the latter was formed byelectrodeposition. Without satisfactory adherence between the foundationmetal and the electrodeposited layer it is not possible to work orfabricate the product, particularly to cold roll, draw or work theproduct without great losses due to the tendency, of the layers to pullapart in spots or to separate altogether.

The problem of electrodepositing an adherent layer of copper on productsmade of stainless alloys of the chromium-nickel, chromium-iron andchromium-nickel-iron types has inspired considerable research, but noneof the processes developed, so far as we are aware, hasb een'ene tirelyconvenient, thoroughly reliable and wholly satisfactory and successfulin practical, commercial and industrial application, especially withlarge articles or products.

We have discovered a process of electrodepositing an adherent coppercoating from tank house or regular copper refinery electrolyte onchromium-containing alloys of the stainless type.

It is an object of the present invention to provide a process ofelectrodepositing an adherent coating of copper from a plating bath oftank house or regular copper refinery electrolyte on a body made ofchromium-containing alloy, such as iron and/or nickel alloys of thestainless type.

It is another object of the invention to provide a process of obtainingan adherent coating of copper by electrodeposition from a plating bathof tank house or regular copper refinery electrolyte on a body made of achromium-containing alloy, such as an alloy of the 80% nickel- 14%chromium-6% iron or stainless steel types,

which body has been pretreated to remove any oxygen-containing or otherpassive film from its surface and then covered with a protective film ofmetal, such as nickel, prior to the copper deposition.

It is a further object of the present invention to provide a process ofelectrodepositing a thick layer of copper from regular copper refineryelectrolyte or tank house electrolyte on a body made from an alloy ofthe nickel-14% chromium-6% iron type or from stainless steel, whichcopper-layer adheres so tightly to the foundation metal that coldrolling and/or drawing do not destroy the bond between them.

It is within the contemplation of the present invention to provideaprocess of electrodepositing an adherent coating of copper from a bathof regular copper refinery or tank house electrolyte on a body made fromchromium-containing alloy of iron and/or nickel, which process iscapable of being practiced on an industrial scale with conventionalappliances and equipment, and which is relatively cheap and permits widecommercial and industrial use.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking, the present invention contemplates a process ofobtaining an adherent coating of copper byv electrodeposition from abath of tank house or regular copper refinery electrolyte upon a bodymade of a chromiumcontaining alloy, such as nickel-chromium alloy,stainless steel or the like, which process comprises the steps ofremoving a passive oxygen-containing or other film from the surface ofthe body to be coated; protecting the body against reformation of such.film by covering it with a film of protective metal, such as nickel,without removing the body from the situs of the first operation;electrodepositing upon the said film of protective metal a thin layer ofcopper from a relatively pure electrolyte; and then transferring thebody to a plating bath of tank house or regular copper refineryelectrolyte where a heavy layer of copper is deposited upon it.

The body of foundation metal to be coated is preferably freed fromgrease in any suitable manner, as those skilled in the art will readilyunderstand, and then immersed in a solution containing hydrochloric acidand nickel chloride where the oxygen-containing or other passive film isremoved. While the body is still immersed in the solution where thepassive film is removed, a layer of nickel is electrodeposited on theactive mation of a passive film when again exposed to air. The body isthen transferred to a relatively pure copper plating bath. low inimpurities, especially antimony, where a thin copper layer iselectro-deposited over the nickel layer. The final deposit of copper ismade in a plating bath of tank house or regular copper refineryelectrolyte to which the copper and nickel coated body is nexttransferred and in which a relatively heavy layer is formed under usualplating conditions.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the following illustrative example isgiven of a preferred procedure of carrying the invention into practice.

A body or article made of a nickel-chromiumiron alloy containing about79% nickel, about 13% chromium and about 7% iron was pumice scrubbeduntil there was no water break. The degreasing and cleaning of thesurface of the body or article may, of course, be accomplished by anyother suitable method as those skilled in the art will understand.

The degreased and cleaned body or article was then immersed in an acidnickel chloride solution having the following composition:

Grams per liter NiCl2.6H2O, about 240 E01, about 36 The temperature ofthe solution was kept at about 70 F. It will be evident that the removalof the passive film could be accomplished in a solution containing nonickel chloride and that this salt could be added thereto in properamount after the passive film had been removed.

The nickel-chromium-iron article or body was made anode to anodicallytreat the surface thereof for about 2 minutes at a current density ofabout amperes per square foot (2.2 amperes per square decimeter) usingnickel electrodes as cathodes. While the article was maintained in thesolution, the current was then reversed and nickel was electrodepositedon the anodically treated surface of the article for about 12 minutes ata current density of about 20 amperes per square foot (2.2 amperes persquare decimeter).

The article now protected by nickel plate was removed from the solutionand transferred without rinsing to an acid copper sulphate platingsolution made from a good grade of sulphuric acid and copper sulphatelow in impurities where a layer of copper about 0.001 inch thick wasdeposited under the following conditions:

Concentration of CuSO4.5HzO, about grams per liter 200 Concentration ofH2804, about do 100 Temperature, about F 70 Current density, aboutamperes per square foot 33 Anodes, pure cathode copper.

2,285,549. alloy surface to protect the body against refor- The processof pretreating the foundation metal comprising immersing a cleanedarticle or body in a nickel chloride-hydrochloric acid bath anddepositing on the active surface thereof a thin film of nickel prior totransferring the body to a copper plating bath, forms the subject matterof the copending application of Andrew Wesley, Serial No. 177,462, filedDecember 1, 1937. The satisfactory adherence of electrodeposited copperto an article made of a chromium containing alloy of the stainlesstype,-e. g., the nickel- 14% chromium or stainless steel types, appearsto depend upon a number of critical conditons, one of which is thesubstantially complete absence of any oxygen-containing or other passivefilm on the surface of the article to be plated. While it is notdiflicult to remove such a film in an acid bath as describedhereinabove, it had been impracticable on an industrial scale to preventreformation of such a film during transfer of the article to the copperplating bath from the film removing solution. The deposition of a filmof protective nickel on the article while it was still in the acid bathin accordance with the process of the said copending applicationsuccessfully prevented reformation of an oxygen-containing film on thearticle during the transfer to the copper plating bath, and asatisfactory bond between the foundation metal and the Copper layer wasobtained as long as the copper platin bath was relatively pure. Whencopper refinery or tank house electrolyte was used, however, it wasfound that the copper layer did not adhere satisfactorily in all cases.

Experiments indicated that a cause of the failure to obtain goodadherence between the nickel coated foundation metal and a copper layerdeposited from tank house or regular copper refinery electrolyte wastraceable to the presence of impurities in the electrolyte in amountssufiicient to impair the bond between the copper layer and the nickelplated body. The impurities may be displaced from solution by action ofthe nickel film present on the foundation metal, resulting in theformation of a non-adherent layer of impurities, or of materialcontaining impurities, on the nickel coated foundation metal. Such afilm of impurities, or of material containing impurities, would preventthe adherence of the subsequently deposited copper layer to the nickelplated foundation metal. By depositing a thin layer of relatively purecopper on the nickel film as hereinbefore described, before the nickelplated body is placed in the bath of tank houseor copper refineryelectrolyte, the formation of a nonadherent film of impurities, or ofmaterial containing impurities, on the nickel and copper plated body iseffectively prevented when the body is transferred to tank house orregular copper refinery electrolyte. As a result, the bond between thecopper layer and the foundation metal is very tenacious and resistsseparation of the layers when the article or body is subsequently coldrolled or drawn.

Tests made to determine the effect of antimony, as an example of animpurity commonly present in tank house or copper refinery electrolyte,upon the adhesion of electrodeposited copper to a nickel plated body ofnickel-chro- 5 mium alloy appear to substantiate the explanation of thephenomenagiven in the preceding paragraph. In conducting these tests,the method employed to determine the adhesion of the copper to thenickel plated body was similar to that described by Mr. Ollard inFaraday Society Transaction, vol. 21,- 1925-26, pp. 81-90, and by Mr.Hothersall in Transactions of the Electrochemical Society, vol. 64,1933, pp. 69-85. Briefly stated, test specimens of an alloy containingabout 79% nickel, 13% chromium and 7% .iron were prepared in the form ofrods 1" in diameter and about 1 long. After cleaning and removing thepassive film as hereinbefore described, the test specimens were coatedwith a thin protective layer of nickel while still immersed in thehydrochloric acid-nickel chloride bath. Test specimens were thentransferred to various copper plating baths having regulated amounts ofantimony dissolved therein and a heavy deposit of copper was plated onan end of each rod. The deposit was somewhat disc shaped and about 1 indiameter and 0.1' thick. When removed from the copper plating bath, thedeposit encircled a portion of the rod and in order to obtain a truevalue of the surface adhesion, the specimens were placed in a lathewhere the deposit was machined off the cylindrical face of the rod toleave a disc shaped deposit adhering to the rod at the end only. A holewas then bored through the deposit into the end of the rod, therebyleaving a ring of copper adhering to the rod by an annulus exactlyacross. The adhesion was determined by measuring the load required todetach the copper ring from the rod. A more complete description of thetest, accompanied by drawings, is contained in the above citedpublications and need not be repeated here as those skilled in the artare familiar with the test. Typical results are set forth in Schedule I.

Rod No. 5 was prepared in the same manner as Rod No. 4 except that alayer of chemically pure copper 0.001 thick was deposited on the nickelplated rod before it was placed in the bath con-- taining 0.6 gram perliter of antimony. When this specimen was placed in the testing machine,

taining iron and/or nickel alloy is not a simple oxide; or thatimpurities in copper refinery or tank house electrolyte other thanantimony may contribute to the formation of a non-adhering film on thenickel plated article when it is placed therein, or otherwise preventthe direct deposition of a satisfactory adherent heavy layer of copperfrom such electrolyte upon the nickel plated body. The present inventionprovides a process whereby-it is possible to obtain a satisfactory andcommercially acceptable adherent copper deposit from tank house orcopper refinery electrolyte on a body or article made of achromium-containing alloy of iron and/or nickel, with standard equipmentand on an industrial scale.

house electrolyte containing antimony in amounts the copper failed at aload of 11,800 pounds per square inch without breaking the bond betweenthe copper and the foundation metal. This phenomenal increase from about80 pounds per square inch on the one hand to more than 12,000 pounds persquare inch on the other demonstrates the value and importance of thepresent invention in assuring strong adhesion between thechromium-containing foundation metal and the copper deposited from tankhouse and copper refinery electrolyte which often contains detrimentalamounts of impurities including antimony.

The copper plating bath in which the nickel plated body ofchromium-containing stainless alloy is given the preliminary thin coppercoating should be low in impurities. Under no circumstances should itcontain over 0.3 gram of antimony per liter and preferably it shouldcontain less than 0.1 gram per liter.

While the foregoing theory is believed to be correct, it is to bedistinctly understood that the invention is not dependent upon anyparticular theory of operation. Thus, it may be that the greater thanabout 0.1 gram per liter to produce a composite body capable of beingworked including cold rolling and drawing which comprises anodicallyactivating a degreased body of nickelchromium alloy at about 20 amperesper square foot for about 2 minutes in an aqueous electrolyte containingabout 36 grams of hydrochloric acid per liter and about 240 grams ofnickel chloride per liter and in the presence of pure nickel electrodesto obtain a body of nickel-chromium alloy having an active surface,reversing the polarity of said body and electrodepositing a film ofnickel on said active surface from said aqueous electrolyte during aperiod of about 2 minutes at a current density of about 20 amperes persquare foot to obtain a body of nickel-chromium alloy having a protectedsurface, without rinsing, transferring said body having a protectedsurface to a first aqueous copper electrolyte containing about 200 gramsof copper sulphate per liter, about grams of sulfuric acid per liter andbeing substantially devoid of antimony in amounts sufilcient to reducethe breaking load of the bond between the body of nickel-chromium alloyand the copper electrodeposited thereupon below about 9000 pounds persquare inch, electrodepositing a film of copper about 0.001 inch thickthereon to obtain a protected body of nickel-chromium alloy having afilm of copper thereon, anodically treating the copper surface of saidprotected body for about 3 minutes at a current density of about 13amperes per square foot in an aqueous impure copper plating electrolytecomprising copper'refinery tankhouse electrolyte, reversing the polarityof said protected body and electrodepositing a relatively thick layer ofcopper from said impure copper electrolyte comprising copper refinerytankhouse electrolyte containing antimony in amounts greater than about0.1 gram per liter to produce a composite body comprising a base ofnickel-chromium alloy, a protective film of nickel, a film of copper,and a relatively thick layer of copper, the bond between said body ofnickel-chromium alloy and said thick layer of copper being capable ofwithstanding a breaking load of at least 9000 pounds per square inch,and cold working said composite body to produce a worked body withoutrupture of the aforesaid bond.

2. A process for utilizing copper refinery tank house electrolytecontaining antimony in amounts greater than about 0.1 gram per liter toproduce a composite body capable of being worked including cold rollingand drawing which comprises anodically activating a degreased bodypassive film that forms on the chromium-conof. nickel-chromium alloy atabout 20 amperes per square foot for about 2 minutes in an aqueous Yelectrolyte containing about 36 grams of hydrochloric acid per liter andabout 240 grams of nickel chloride per liter to obtain a body ofnickel-chromium alloy having an active surface, reversing the polarityof said anodically activated body and electrodepositing a film of nickelon said active surface from said aqueous electrolyte, said film ofnickel being at least that amount deposited by passing a current of 20amperes per square foot for six minutes to provide a body ofnickel-chromium alloy having a protected surface, electrodepositing afilm of copper at least about 0.001 inch thick from a first aqueouscopper electrolyte containing about 200 grams of copper sulphate perliter, about 100 grams of sulfuric acid per liter and beingsubstantially devoid of antimony in amounts sufilcient to reduce thebreaking load of the bond between the body of nickel-chromium alloy andthe copper electrodeposited therefrom below about 9000 pounds per squareinch to obtain a protected body of nickelchromium alloy having a thinfilm of copper, electrodepositing a relatively thick layer of copperfrom an impure copper electrolyte comprising copper refinery tankhouseelectrolyte containing antimony in amounts greater than about 0.1gramper liter to obtain a composite body comprising a base ofnickel-chromium alloy, a protectivefilm of nickel, a film of copper anda relatively thick layer of copper, the bond between said Tbody ofnickel-chromium alloy and said copper being capable of withstanding abreaking load of at least 9000 pounds per square inch, cold rolling saidcomposite body, and deep drawing said cold rolled composite body toproduce a rolled,.drawn body without rupture of the aforesaid bond.

3. A process for utilizing copper refinery tankhouse electrolytecontaining antimony in amounts greater than about 0.1 gram per liter inthe production of a,composi'te body capable of being. worked includingcold rolling and drawing which comprises anodically activating adegreased body of nickel-chromium alloy at a current density of about 20amperes per square foot in'an aqueous electrolyte containing about 36grams of hydrochloric acid per liter to obtain a nickel-chromium bodyhaving an active surface capable of receiving an adherentelectrodeposited film of nickel, electrodepositing a film of nickel onsaid nickel-chromium body while immersed in said aqueous electrolyte andin the presence of about 240 grams of nickel chloride per liter, saidfilm of nickel being of sufficient thickness to provide a protectednickel-chromium body, i electrodepositing a film of copper about 0.001inch thick from a first aqueous copper electroplating electrolytesubstantially devoid of antimony to produce a protected nickel-chromiumalloy body having a film of nickel thereon and a superimposed film ofcopper, and electrodepositing a thick layer of copper on said protectednickel-chromium alloy body from a second aqueous impure copperelectroplating electrolyte comprising copper refinery tankhouseelectrolyte containing antimony in excess of 0.1 gram per liter toobtain a composite body comprising a base of nickel-chromium alloy, aprotective film of electrodeposited nickel, a film of electrodepositedcopper, and a thick layer of electrodeposited copper, the bond betweensaid thick layer of copper and said base being capable of withstanding abreaking load in excess of about 9000 pounds per square inch and beingcapable of withstanding the stresses of cold working including coldrolling and drawing without rupture of the aforesaid bond.

4. The process set forth in claim 3 wherein the first aqueous copperelectroplating electrolyte substantially devoid of antimony ismaintained at a temperature of about F.

5. The process set forth in claim 3 wherein the first aqueous copperelectroplating electrolyte substantially devoid of antimony contains notmore than about 0.1 gram of antimony per liter.

6. The process set forth in claim 3 wherein the both! of nickel-chromiumalloy is selected from the group consisting of stainless steel and anickel-chromium-iron alloy consisting of about nickel, 14% chromium an6% iron.

- ANDREW WESLEY.

HARRY R. COPSON.

